Hi, I have a 2005 Crew Cab LE. It has the overdive button on the automatic shifter. I remeber reading things about this but can anyone explain to me what this button actually does. I know when you press it the light on the dash turns on telling you its off, seems rahter reversed. I swear i read someone was getting better mpg if they didnt have it on all the time. So what does it actually do? Thanks.

I'm not sure how someone would get better gas mileage by turing off 5th gear on their 5 speed automatic! But, that's all it does. If you were towing a trailer in a hilly area and your transmission kept shifting from 5th to 4th and back due to the terrain and load, it's recommended to turn it off and drive in 4th gear to save wear and tear on the transmission, but other than that, I would leave it on.

The button turns off the overdrive function, which limits the operation of the transmission to gears 1-4. The truck will not shift into the highest gear (5th gear) when the overdrive button is used to turn O/D off. So, 05 NISMO 4x4 is right -- it's hard to believe anyone could actually get better gas mileage by turning the O/D off.

The term "overdrive" refers to a gear that is designed to set a final drive ratio to less than 1.0. Thus, the output driveshaft from the transmission is actually turning faster than the engine when an overdrive is engaged.

The O/D helps with better highway mpg when the vehichle is traveling at high, constant speeds where little torque is needed. However, if something is being towed or if the vehicle is going over hilly terrain, the transmission will likely have to constantly downshift from 5th gear to provide enough torque to keep the vehicle from slowing down. This isn't good for the transmission, and can cause the transmission to heat up quite a bit. That's why it should be turned off under such conditions.

Another occasion to hit the button and turn off the O/D -- I have found that while cruising at about 40 mph under a very light throttle the truck will go in and out of 5th gear with every little modulation of the gas pedal. (Squeeze the gas it downshifts to 4th, let up on gas it upshifts to 5th, over and over and over.) Punch the button, it stays in 4th, the tranny is happy.

It does it mostly when I'm in traffic since I'm on/off the gas moving with the traffic. If I'm the only car out there and cruising STEADY at 40 then it doesn't do it much. 40 mph seems to be right at a 4-5 shift point under part throttle.

Another occasion to hit the button and turn off the O/D -- I have found that while cruising at about 40 mph under a very light throttle the truck will go in and out of 5th gear with every little modulation of the gas pedal. (Squeeze the gas it downshifts to 4th, let up on gas it upshifts to 5th, over and over and over.) Punch the button, it stays in 4th, the tranny is happy.

It does it mostly when I'm in traffic since I'm on/off the gas moving with the traffic. If I'm the only car out there and cruising STEADY at 40 then it doesn't do it much. 40 mph seems to be right at a 4-5 shift point under part throttle.

Good point. I've actually done the same thing on a couple of occasions.

Q-Tip, thanks for the tip, next time I am in traffic I will make sure to look and see if the truck keeps shifting between the 2. Can I pop in and out of O/D at any speed? If I was in 4th and wanted to turn the O/D off (like if the traffic cleared up) can I just turn the O/D off and it will shift and be fine?

Q-Tip, thanks for the tip, next time I am in traffic I will make sure to look and see if the truck keeps shifting between the 2. Can I pop in and out of O/D at any speed? If I was in 4th and wanted to turn the O/D off (like if the traffic cleared up) can I just turn the O/D off and it will shift and be fine?

Yup on both accounts. Just punch the button and it toggles the O/D on and off at whatever speed you are traveling. I've done it at highway speeds with no problem. If you are in 5th gear (O/D) it will kick down to 4th (watch the display on the dash - will change from D to 4). It will kick down and the revs will increase, but unless you are going 110 mph or something it won't blow up anything.

If you are at a stop or are traveling slowly when you hit the button then it will shift normally but won't go into 5th when you get up to speed. Again, watch the dash display - if the O/D OFF light is on and the gear indicator says 4 then it will NOT go into 5th.

Not only do I turn off the overdrive in hilly terrain or while towing, I just down shift manually quite a bit when off roading as well. If I know that I will not go past 25mph I stay in third or below. I just don't like my tranny shifting up and down constantly. And yes, she will heat up and wear and tear is increased. Shifting also requires energy, this is why a manual tranny produces better gas mileage. As long as I stay around 1500-2000 rpm, I will keep her at the appropriate gear.